Extracorporeal photopheresis (ECP) is a specialized medical procedure that treats certain immune system conditions. This non-surgical therapy is used when other treatments are unsuccessful or unsuitable. It involves processing a patient’s blood outside the body to modify specific immune cells. ECP offers a targeted approach to managing complex immune-mediated diseases.
Understanding Graft-versus-Host Disease
Graft-versus-Host Disease (GVHD) is a complication that can arise after an allogeneic stem cell or bone marrow transplant. In these transplants, a patient receives healthy blood-forming cells from a donor. The donor’s immune cells may recognize the recipient’s tissues as foreign and attack them.
GVHD presents in two forms: acute and chronic. Acute GVHD typically occurs within the first 100 days following a transplant. It commonly affects the skin, causing rashes, itching, and redness. It can also impact the gastrointestinal tract, leading to nausea, vomiting, and diarrhea, and the liver, potentially causing jaundice.
Chronic GVHD usually develops more than 100 days after a transplant and can persist for an extended period. This form can be widespread, affecting organs including the skin, mouth, eyes, lungs, and joints. Common manifestations include skin changes, dry eyes, dry mouth, and shortness of breath. Both acute and chronic GVHD can range from mild to severe.
The Extracorporeal Photopheresis Procedure
Extracorporeal photopheresis (ECP) is an outpatient procedure. It begins with drawing blood from the patient, typically through a vein or a central line. This blood then goes into an apheresis machine, which separates its components.
Within the machine, white blood cells, particularly lymphocytes, are isolated from red blood cells, plasma, and platelets. The separated white blood cells are then mixed with a light-sensitive medication, such as psoralen. This mixture is exposed to ultraviolet A (UVA) light within a chamber. The UVA light activates the medication, which interacts with the treated cells.
Finally, these treated white blood cells are reinfused back into the patient’s bloodstream, while untreated red blood cells and plasma are returned simultaneously. The procedure generally takes 2 to 4 hours.
How ECP Modulates the Immune System
ECP modulates the immune system. The treated white blood cells, once returned to the body, undergo programmed cell death, or apoptosis. This cell death results from the interaction between the light-sensitive medication and UVA light, which damages the DNA within these cells.
The body’s immune system processes these apoptotic cells. This may lead to a “re-education” or “reprogramming” of other immune cells, promoting the generation of regulatory T-cells (Tregs). These Tregs suppress harmful immune responses and foster immune tolerance, helping the immune system distinguish between healthy tissues and foreign cells. By increasing these regulatory cells and decreasing pro-inflammatory signals, ECP helps reduce the immune attack in GVHD.
Treatment Process and Patient Outcomes
ECP is typically administered as a series of treatments, not a single session. Patients often undergo treatment on two consecutive days, with sessions repeated weekly or bi-weekly for several months. The frequency and duration depend on the patient’s condition, GVHD severity, and response to therapy.
ECP is frequently used as a second-line treatment for GVHD cases that have not responded to initial steroid therapy, or when steroids cause side effects. Patients may experience mild, temporary side effects, such as fatigue, dizziness, or nausea after the procedure. The medication makes patients sensitive to sunlight for about 24 hours, requiring precautions like wearing sunglasses and avoiding direct sun exposure. Improvement with ECP is often gradual, taking several months to observe results. The treatment may reduce reliance on other immunosuppressive medications.